1. Field of the Invention
The present invention relates to a system and a method for the fertilization of plants, including ornamental and horticultural plants, crops, grasses, transplants and turf systems. In particular, the invention relates to the use of a spatially localized, banded phosphorus solid-phase buffered system for the reduction of phosphorus in high-phosphorus media and regulation of phosphorus levels in media generally.
2. Description of Related Art
Plants coordinate and regulate their growth in response to environmental signals, including light, water and nutrients. Phosphorus (P) is one of the essential mineral macronutrients that is directly involved in plant metabolism and cannot be replaced by other elements. In the absence of P, a plant will not be able to complete its life cycle. Furthermore, P is a nutrient that is required in higher amounts for optimal plant growth, including root growth, root branching, shoot growth and branching, leaf and stem expansion, and reproductive development. Precise control of P availability, as is made possible by aluminum buffering, permits the manipulation of plant growth in horticulture and agriculture. For example, it is desirable to control the size and shape of the shoot system in the production and cultivation of many plants, including turf, transplants, and flowering ornamentals. In such cases excessive shoot growth reduces product quality or appearance, or increases maintenance requirements.
The use of low levels of P, for example, less than 100 micromolar phosphate, permits the cultivation of plants at a rapid rate of overall biomass accumulation without excessive shoot growth. Growers often desire a well-developed, highly branched root system, especially in the production of plants that will be transplanted into soil after production, including bedding plants, nursery ornamentals, woody plant and tree seedlings, and commercial vegetable transplants. Furthermore, the use of low levels of P also promotes root branching.
The main driving force for moving P to the root surface is diffusion. Diffusion occurs when ions move from a region of higher concentration to lower concentration. Diffusion through a short distance is much faster than through a long distance because the time required for a substance to diffuse a given distance is determined by the square of the distance. This suggests that the uptake of a certain nutrient by diffusion is strongly related to available ions close to the root surface. P is usually stabilized in soils and tends to be less mobile compared to other nutrients.
Aluminum (Al) is not an essential element for plant growth. Most plants are sensitive to high Al concentrations. Al interferes with the uptake of P directly through the precipitation of aluminum phosphate, because P is bound by strong P adsorption to clay minerals. Since Al is immobile in plant tissue, it is seldom transported to shoots and the accumulation is mostly confined to the roots.
A solid-phase fertilizer/buffer made from aluminum oxide pellets (alumina, Al2O3) and P, collectively, Al—P, was originally developed for a P nutrition study in a container system using sand as the growing medium. The purpose of using Al—P was to simulate a realistic supply in the controlled environment. Coltman et al. (Am. Soc. Hort. Sci., 107:938-942, 1982) first developed the sand-alumina culture system with P supplied from the P-absorbed alumina, which was obtained from activated alumina loaded with phosphate (KH2PO4). This sand-alumina culture technique not only showed promise for simulating plant responses to P concentrations under conditions comparable to those found in soils, but also provided a range of stable and reproducible P concentrations for a more ideal experimental medium. It has been found that the P concentration desorbed from sand-alumina is dependent on the P concentration loaded on the alumina, and that after the stability of solution P concentration in the culture has been reached, increasing the density of P-loaded alumina in the sand has no effect on the average culture P concentration. Thus, diffusion, the rate-limiting step in the uptake of P from soil, appears to be rate-limiting in a sand-alumina system as well. Additionally, the extent of the diffusion-limitation can be manipulated by changing alumina density (Coltman et al., 1982).
U.S. Pat. No. 5,693,119 to Lynch et al. (incorporated herein by reference) discloses the use of P fixed to Al (Al—P) in soil-less-growing media, such as peat, vermiculite, perlite, and mixtures thereof. The '119 patent discloses that the soil-less container system with Al—P displays greatly reduced P leaching from the container and plants display growth that is equivalent or superior to that of plants grown with conventional fertilizers. However, the '119 patent does not disclose the application of an Al—P system to anything other than a low-soil or soil-less container system.
U.S. Pat. No. 6,287,357 to Lynch et al. (incorporated herein by reference) describes the use of Al—P as a fertilizer and P buffer in soils, which is especially useful for plants grown in low P soils. The Al—P is applied to soils, wherein the P bound to the alumina is desorbed and released into the soil in a sustained fashion, thereby supplying a consistent supply of P to the plants. Thus, the '357 patent is directed to applying P to soil. It is not directed, however, to soils already containing high or optimal levels of P or to systems that contain anything other than Al—P fertilizer.
More importantly, the above-mentioned patents do not disclose the concepts of spatially positioning, i.e., banding, a P supply to encourage root growth in a desired plant species, or of placing P at a location in the root zone where certain invasive species cannot access the nutrient, thereby selectively encouraging plant growth of desired species.
A number of problems are associated with traditional sustained and/or intensive P fertilization of soils. One problem is that P, through leaching or runoff, may find its way to rivers, streams, estuaries and other bodies of water, where it poses risks to humans and the environment. Because biological activity in many aquatic systems is limited by low P availability, this influx of P creates algal blooms and other biological responses that are generally detrimental. P pollution of water resources and natural ecosystems is one of the principal health and environmental concerns associated with agriculture in the United States and other industrialized nations. A number of solutions have been applied to this problem, such as reduction of fertilizer application, reduction of erosion and runoff from agricultural lands through contour terracing, riparian green strips and retention ponds, as well as the use of technologies, such as coated fertilizers that may release P more slowly into the soil. These methods, however, are expensive and require a high level of expertise or sophistication in monitoring the P content of the soil and the leachate.
Another problem associated with typical P fertilization methods used in agricultural, horticultural, residential and municipal settings is the periodic high soil P availability that results from the fertilization methods, which may have detrimental effects on plant growth by reducing root growth and by creating nutritional imbalances with other essential nutrients, such as calcium, zinc and iron. Currently available P fertilizers and methods for fertilizing soils do not adequately synchronize the P-supplying capacity of the soil with the P demand of growing plants. Many technologies have been employed to address this problem, and some are effective to a limited extent. However, such approaches typically require significant expense by the grower, expertise or sophistication in monitoring the nutritional requirements of a growing crop to avoid deficits, or they may not be well suited to soils of inherently low P retention capacity, such as sandy soils, organic soils, and soils that are already saturated with P from previous P applications. For example, the use of “slow release” P fertilizers, such as Osmocote, a resin-coated fertilizer, is not always optimal because these products release P as a function of water content of the soil, temperature of the soil, and time, which may not be directly associated with the timing of the nutritional requirements of the crop.
There is a need for an environmentally friendly means of limiting the growth of non-desired plant species. Current plant management techniques rely on herbicides, pesticides, plant growth regulators, etc., which often pollute soil and water and which may have carcinogenic and teratogenic effects on humans and other mammalian species. The elimination or reduction of such chemicals would reduce the burden on the environment and the financial cost borne by farmers, golf courses, municipalities and other landholders.
There also is a need for a means of improving the drought tolerance/resistance of plants, particularly in regions where water is a scarce resource, e.g., the sunbelt, or in areas undergoing desertification due to human disruption.
Thus, there exists a need to provide field crops, plants, and grasses with a suitable level of P that is responsive to the needs of the growing vegetation, while minimizing P leaching from media and minimizing contamination of the surface runoff with P. In particular, a need exists to provide a steady source of P to plant roots in any type of media, including turfgrass systems grown on constructed media. Presently, there is lacking a way to accomplish this in a cost-effective manner and in a manner that is equally applicable to the wide variety of media, crops and grasses in need of P regulation, while at the same time minimizing the potentially detrimental effects high P media levels can have on plant growth, human health and the environment.